各種鋳鉄のフェライト化過程にみられる収縮について

抄録

  In the early stage of ferritizing of cast irons, contraction is observed instead of expansion, which generally results from the graphitization of cementite. Using the dilatometric method, the conditions giving rise to contraction and mechanisms operating on this phenomenon were investigated. The contraction in ferritizing is affected remarkably by the thermal history. In the pearlitic cast iron, which is austenitized from ferritic iron and then air cooled, the early stage contraction in ferritizing is very distinguished and the final expansion is very little. The contraction becomes gradually remarkable changing from flaky to spheroidal graphite, and the lower the silicon content is, the more contraction is obtained. This phenomenon is explained to be as follows; in the austenitizing of ferritic cast iron, the graphite becomes porous due to the increasing vacancies formed by the Kirkendall effect, which results in the observed expansion. The porosities are retained in air cooled iron and decrease as carbon from graphitizing of cementite fills the porosities during the ferritizing process This results in contraction.